Conventionally, in HSDPA (High-Speed Downlink Packet Access) of 3GPP (3rd Generation Partnership Project), for high-speed downlink packet transmission, adaptive modulation in which a base station apparatus adaptively controls a modulation scheme used in a radio communication terminal apparatus according to a state of the propagation path, and scheduling in which the base station apparatus selects a radio communication terminal apparatus with a relatively good state of the propagation path to transmit a signal, are used. Further, in multicarrier transmission schemes such as OFDM (Orthogonal Frequency Division Multiplexing) and MC-CDMA (Multi Carrier-Code Division Multiple Access) under review as a transmission scheme in beyond 3G mobile communication system, high-speed transmission is implemented using a plurality of subcarriers.
In these multicarrier transmission schemes, since adaptive modulation and scheduling are performed for each subcarrier of a multicarrier signal, the radio communication terminal apparatus needs to notify instantaneous channel quality information (CQI: Channel Quality Indicator) of each subcarrier to the base station apparatus. Accordingly, in the multicarrier transmission system where adaptive modulation and scheduling are performed, each of a plurality of radio communication terminal apparatuses notifies CQIs of all the subcarriers in a downlink multicarrier signal to the base station apparatus, and the base station apparatus receiving the notifications, determines subcarriers, modulation scheme and coding rate in a downlink multicarrier signal to be transmitted to each of the radio communication terminal apparatuses using a predetermined scheduling algorithm with taken into consideration the CQIs from each of the radio communication terminal apparatuses.
When a base station apparatus simultaneously transmits downlink multicarrier signals to a plurality of radio communication terminal apparatuses in such a multicarrier transmission system, the base station apparatus performs frequency scheduling using CQIs for each subcarrier of downlink multicarrier signals transmitted from all the radio communication terminal apparatuses, assigns subcarriers of the downlink multicarrier signal with relatively good states of the propagation path to each of the plurality of radio communication terminal apparatuses, and determines a modulation scheme and coding rate so as to meet a predetermined packet error rate in the state of the propagation path.
Herein, in the multicarrier transmission system for performing adaptive modulation and scheduling, for example, when a downlink multicarrier signal is made up of sixty-four subcarriers, each radio communication terminal apparatus notifies sixty-four CQIs to the base station apparatus. Further, when each of sixty-four CQIs is expressed by five bits, each radio communication terminal apparatus needs to transmit 320 bits (=5 bits×64) of reception quality data for each downlink multicarrier signal in a single uplink multicarrier signal to the base station apparatus.
Non-patent Document 1: Hara, Kawabata, Duan, Sekiguchi, “MC-CDM System for Packet Communications Using Frequency Scheduling”, Technical Report, July, 2002, RCS2002-129, pp. 61-pp. 66.